Heating element



I 06f 25, 1949 c. H. sPARKLlN 2,485,672

HEATING ELEMENT Filed Sept. 6, 1946 Patented Oct. 25, 1949 UNITED STATESPATENT OFFICE HEATING ELEMENT Charles H. Sparklin, Chicago, Ill.,assignor to Birtman Electric Company, a corporation of Illinois 7Claims.

This invention relates to a heating element, and particularly to aresistance heating element of the type used to heat the sole plate of anelec- ,tric iron.

Various methods of combining a resistance heating element with anelectric iron sole plate have been employed in the past. These includeimbedding the resistance element in mud on top of the sole plate of theiron, providing a resistance element in the form of a rod Which wasanchored on top of the sole plate, and pressing the resistance elementor unit in grooves in the surface of the sole plate. Variousdifficulties were encountered with these prior methods, however, as insome the resistance element could not withstand 1 the physical shock towhich the electric iron was subjected, and in others uneven heatingoccurred.

In applicants copending application Serial No. 637,581, filed December28, 1945, there is shown a resistance element whose core is a flat stripof mica or the like having a generally flattened cross-section which maybe rectangular or rounded at top, bottom, or sides, or any combinationof these. This strip is wound with a tape of resistance material. Theelement is held in a groove in the sole plate formed by upstanding angesand is surrounded by insulating material, preferably in powdered form. Acover plate is positioned on top of the insulating material in contacttherewith and completely closes the groove.Y The sole plates areordinarily formed of cast aluminum with the flanges forming a part ofthe sole plate. It was discovered in actual practice that the grooveswere seldom uniform in width and that when the cover plate was placed inposition over the insulating material it was in some places too narrowand in others did not extend completely across the groove. Thispermitted leakage of the granular insulating material. In order toovercome this I have invented a different type of cover plate thatautomatically seals the space between the flanges even though theflanges are not uniformly parallel to each other and may vary in widthfrom one iron to another.

It was also discovered in earlier forms of heating elements that theends of the resistance wire that extended out the ends of the groovewere liable to become broken, thereby necessitating replacement of theentire resistance element. It has been found that a superior type ofiron can be made if the anges forming the sides of the groove at the endthereof are tapered toward wire within the tapered end of the groove issurrounded with insulating material that is held in place by an extendedend of the cover plate. The end of the cover plate is tapered in amanner similar to the tapering of the groove.

The invention will be described as related to the embodiment shown inthe accompanying drawings. Of the drawings Fig. 1 is a plan View of asole plate having a V-shaped groove therein; Fig. 2 is a plan view of acover plate for sealing the groove; Fig. 3 is a vertical section showingthe cover plate in position to be pressed downwardly within the groove;Fig. 4 is a vertical section similar to Fig. 3 showing the cover platein place and a resistance element within the groove; and Fig. 5 is avertical section taken through a tapered end of the groove showing thecover plate in each other. In this construction the end of the place.

The sole plate I0 of an electric iron is formed with a continuousV-shaped groove II therein bounded by upstanding flanges I2. The ends I3of the V-shaped groove II are tapered with the ends I4 of the anges I2being closer together than are the flanges at the main body portion ofof the groove. A similarly shaped cover plate I5 is provided with theedges I6 of the cover plate bent upwardly and outwardly.

The resistance element I'I comprises a iiat resistance wire I8 wound ona flat mica core I9. This resistance element is held within the groove II and insulated therefrom by powdered insulating material 20. Theconstruction of the insulating .element and the arrangement and type ofinsulating material as well as the method of construction is describedin greater detail in my aforementioned copending application 637,581.

When the resistance element and insulating material have been pressedwithin the groove II the cover plate I5 is arranged as shown in Fig. 3.In this cover plate the distance between the bottom of the bent edges I6is slightly less than the width of the narrowest portion of thenarrowest groove II which will be encountered in actual manufacture. Thedistance between the tops of the edges I6 is slightly greater than thewidth of the widest part of the widest groove I I so encountered. Thecover plate I5 is ordinarily made of a metal, such as aluminum, and isusually approximately ,1-6 thick. The edges I6 are bent so that theradius of curvature at the bent line is approximately equal to thethickness of the plate. Each edge I6 extends upwardly above the top ofthe remainder of the plate a distance equal to at least twice thethickness thereof, as is shown in Figs. 3, 4 and 5.

plate A force is applied to the cover plate I5 and it is pushed downinto the groove II. This force causes the bent edges I6 to be bentfurther toward each other, as is shown in Fig. 4. Because the coverplate is made of very thin material it adapts itself to the groove I Iand closes the groove completely even though the inner sides of theflanges I2 are not exactly parallel. The cover plate is held in place bydisplacing small portions 2l of metal inwardly along the top edges ofthe flanges I2, as shown at 2| and as described in my aforementionedpatent application. These displaced portions of metal are located abovethe tops of the bent edges I6, as shown in Figs. 4 and 5.

The end 22 of the resistance wire held within the tapered ends I3 of thegroove is surrounded by three layers of fiber glass 23, having theability to withstand a temperture of 1200 to 1400 F. The fiber glass isinsulated from the bottom of the groove and the bottom of the coverplate I5 by thin sheets of mica 24. The fiber glass is compressed uponthe wire by the pressure of the I5. This construction serves to anchorfirmly the ends of the resistance wire, and prevents their accidentalbreaking.

Having described my invention as related to the embodiment shown in theaccompanying drawings it is my intention that the invention be notlimited by any of the details of description unless otherwise specified,but rather be construed broadly within its spirit and scope as set outin the accompanying claims.

I claim:

1. A heating element comprising a metal plate, an elongated groovetherein bounded by upstanding flanges, said groove having a tapered end,a resistance element within the groove comprising a resistance wirearound a solid core with the end of said reistance wire extending outthe tapered end of the groove and the core extending only to thebeginning of the tapered end, a thin layer of insulating materialsurrounding the resistance element, core and said end of the resistanceelement, and a metal cover plate contacting the insulating material andheld by the flanges, said cover plate comprising a thin metal platehaving bent upstanding edges contacting said flanges and distortedtoward each other by pressure of the flanges against said edges.

2. The heating element of claim 1 wherein the insulating material aroundsaid core is a powdered material while the insulating material in saidtapered end is a solid with the end of the wire held therein.

3. The heating element of claim 1 wherein the insulating material aroundsaid core is a powdered material while the insulating materia1 in saidtapered end comprises fiber glass, said ber glass being around the Wireand insulated from the bottom of the groove and the bottom of the coverplate by separate insulating material.

4. The heating element of claim 1 wherein the insulating materialsurrounding said core is a powdered material while the insulatingmaterial in said tapered end comprises fiber glass, said fiber glassbeing around the wire and insulated from the bottom of the groove andthe bottom of the cover plate by thin sheets of mica.

5. In a heating element comprising a metal plate, an elongated groovetherein bounded by upstanding flanges, a resistance element therein, anda thin layer of powdered insulating material surrounding the resistanceelement, a metal cover plate contacting the insulating material andpressed against the anges at both sides at all peripheral points abovethe insulating material, said cover plate comprising a thin metal platehaving a body portion and bent upstanding edges at the sides thereofwith each edge extending upwardly above the top of the body portion adistance equal to at least twice the thickness of the body portion andsaid edges bearing against the inner surface of said flanges to form atight seal therewith.

6. The heating element of claim 5 wherein the distance between thebottoms of the bent edges of the cover plate is slightly less at allpoints than the distance between said flanges at corresponding points,and the distance between the tops of said edges is normally slightlygreater than the distance between said flanges at corresponding points.

7. The heating element of claim 5 wherein the tops of the bent edges ofthe cover plate are located below the tops of the flanges, and the coverplate is held in place by metal displaced inwardly from the flanges atpoints above the tops of said edges.

CHARLES H. SPARKLIN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,520,913 Simon Dec. 30, 19241,979,631 Maurer Nov. 6, 1934 2,053,933 Abbott Sept. 8, 1936 2,222,192Arnold et al Nov. 19, 1940 2,277,439 Jepson Mar. 24, 1942

